HU215459B - Cathode for generating hydrogen from alkaline solutions and process for preparing cathode - Google Patents

Abstract

The cathodes of the present invention consist of an electrically conductive heat bath and an electro-catalytic galvanically deposited bath. The electroplating bath, in addition to the metal or metal alloy forming the impregnation, has an average diameter of 0.01 to 150 mm of pendant electrically catalyzed material, or of the metallic saline in platinum powder, plus zinc, cadmium, vanadium, sulfur, containing tin, arsenic, antimony, bismuth, or stoneware from 0.005 to 2000 ppm. When used in a chlorine alkali cell with a cathode-membrane or diaphragm according to the invention, they are low-tube hydrogen-overvoltage, do not change over time and are essentially immune to iron, mercury or other contaminating metal in the alkaline soil. The invention also relates to the preparation of the above cathodes. ŕ

Description

The present invention relates to a process for the preparation of cathodes for the production of hydrogen gas from alkaline solutions containing toxic metals. The electrodes of the present invention are used, in particular, as a cathode in the formation of hydrogen in the presence of an ion exchange membrane or a permeable diaphragm cell for electrolysis of alkali metal halides, in particular in the presence of an alkali metal hydroxide solution.

The invention also relates to an electrode according to the invention.

The main requirement for industrial cathodes is low hydrogen surge, which results in reduced power consumption; as well as adequate mechanical stability against the effects of stress during assembly and fluid turbulence during operation.

The foregoing requirements are met by cathodes consisting of an electrocatalytic conductive coating on a support made of a suitable conductive material, such as iron, steel, stainless steel, nickel and nickel alloy, copper and copper alloy. The electrocatalytic conductive coating may be formed, among other methods, by galvanically or non-electrolytically depositing electrically conductive metals or metal alloys which are themselves only partially electrocatalytic, such as nickel or its alloys, copper or its alloys, silver or alloys, containing metals as a homogeneous phase, most probably in the form of a solid solution.

Other methods include thermal decomposition of the appropriate paint containing the precursor material of the coating material as disclosed in Hungarian Patent No. 158,749 and laser disintegration of such paint as disclosed in U.S. Patent 4,359,436.

Alternatively, the electrocatalytic coating may be formed by galvanically or non-electrolytically depositing electrically conductive metals or metal alloys which are themselves only partially electrocatalytic, such as nickel, copper, silver or their alloys, and which contain a low hydrogen surge electrocatalytic material. Electrocatalytic particles can be elements such as titanium, zirconium, niobium, hafnium, tantalum, metals of the platinum group, nickel, cobalt, tin, manganese as metals or their alloys or oxides, mixed oxides, borides, nitrides, carbides. These materials are added to and kept in suspension in the galvanic bath used to apply the coating.

One of the non-electrolytic deposition methods is the formation of a metal coating, such as a nickel coating, from a solution containing metal ions (e.g., nickel ions) by the addition of chemical reducing agents. The effect of these agents is similar to that of current in the galvanic system, that is, the conversion of metal ions into the corresponding metal. Alternatively, the coating may be formed by a method other than electrolytic, such as flame or plasma spraying, in which a suitable metal wire or powder is applied to the substrate.

It will be seen from the foregoing that the metal coatings of the present invention may be formed by various processes, each of which may be made into the same article.

Coated electrodes with dispersed electrocatalytic particles are described in Belgian Patent Application No. 848,458, corresponding to Italian Patent Application No. 29,506 A / 76, and in U.S. Patent No. 4,465,580. These electrodes are incorporated herein by reference.

German Patent Application No. 31 32269 discloses the application of catalytic coatings from a bath containing suspended carbon particles to achieve a longer service life. The improved service life is attributed to improved mechanical stability against the mechanical action of the formation and separation of hydrogen bubbles. This result is achieved by the hardening of the formed coating and the better adhesion to the substrate than previously known. These characteristics are achieved by adding to the galvanic bath a suitable element, such as silver, copper, molybdenum, tin, lead and / or bismuth, in an amount of 1 to 49% by weight, and by adding silver, copper, tin, platinum or palladium to the catalytic activity of the cathode. improvement. It is specifically mentioned that the addition of too small a quantity does not affect adhesion and hardness, while the addition of too much reduces the corrosion resistance.

JP 59-25987 discloses the preparation of a coating for chlor-alkali electrolysis. The coating consists of a layer of galvanic tails deposited of metals or oxides of the silver and platinum groups and electrically conductive dispersed particles.

EPA 10129231 A1 discloses an anterior low hydrogen cathode cathode consisting of a coating applied to a suitable electrode base by plasma spraying. The coating consists only of electrocatalytic and electrically conductive particles. As shown in Example 1, these are nickel particles mixed with nickel / ruthenium particles. In a further embodiment, the coating is electrolytically applied from a nickel galvanic bath containing a three component Raney nickel alloy dispersed on an electrode substrate.

From the above analysis it can be seen that the pursuit of anteriorities is directed towards the production of cathodes with improved catalytic activity and optionally improved mechanical stability.

In the solutions according to the anteriorities raised, no effort has been made to reduce the toxic effect of the small amount of impurities present in the alkaline solution on the catalytic surface of the cathode. The metal impurities present in the alkali diffuse into the cathode surface and rapidly precipitate upon electrical action in the metal state, thereby causing the catalytic aging of the electrode. Because the alkaline solutions used in industrial plants always contain such impurities in the ppm range, the cathode is deactivated in a relatively short period of time and may need to be replaced sooner than expected. Accordingly, the object of the present invention is not to improve the catalytic activity of the cathode, but to improve its quality.

EN 215 459 Β which is significantly different from the anteriority objective, where the problem of poisoning is not at all raised.

A particularly serious disadvantage of the above-described electrodes is that when used in alkali halide electrolysis in diaphragm or ion-exchange membrane cells, the metal ions in the electrolyte are progressively poisoned, which results in a gradual increase in hydrogen surge. This adversely affects the efficiency of the process, and this extremely critical problem necessitates periodic replacement of the cathode.

Common metal contaminants responsible for poisoning are iron, cobalt, nickel, lead, mercury, tin, antimony, or the like.

In the case of electrolysis of saline in a membrane cell, the metal contamination is usually represented by iron and mercury.

Iron pollution can have two origins:

- chemically derived from the anolyte where the crude salt contains potassium ferrocyanide as an anti-caking additive, and

- electrochemical, due to corrosion of the steel structures of the cathode and its accessories.

Mercury is present in the salt stream after converting the mercury cell into a membrane cell.

As these impurities, usually present in solution in complex form, diffuse to the surface of the cathode, they are easily electroplated and thus form a weak electrocatalytic layer in a relatively short period of time.

This catalytic aging, which depends on many factors, such as the type (composition and structure) of the cathode, the operating conditions (temperature, catholyte concentration) and the nature of the impurities, even after a short operating time and even in the presence of a few ppm impurities. after significant and irreversible.

In view of these fundamental practical shortcomings, the behavior of a plurality of electrocatalytic coated cathodes of various compositions has been studied and, unexpectedly, it has been found that the addition of certain compounds to the above-described and referred to prior art coating electrodes results in low hydrogen over-voltage electrodes. even in the presence of impurities in the electrolysis solution remain stable or near stable. In particular, it has been found that the electrodes of the present invention are practically protected against iron and mercury poisoning by their electrocatalytic coating. This is accomplished by adding 0.005-2000 ppm of additive to the galvanic bath used for coating. In the remainder of the specification and in the examples, the coating thus prepared is referred to as an "additive" coating. Elements which, when used as an additive, increase the coating's resistance to poisoning are classified in Groups IB, IIB, IIIA, IVA, VA, VB, VIA, VIB and VIII of the Periodic Table, hereinafter referred to as "additives".

Specifically, for the preparation of cathodes having electrocatalytic coatings which contain dispersed particles of electrocatalytic material

i) degreasing the electrically conductive support, and ii) etching the electrically conductive support with acid or electrolytically, iii) electroconductive support comprising metal ions and suspended electrocatalytic material particles having an average diameter of 0.01 to 150 µm for forming a metal or metal alloy coating. immersing in a galvanizing coating bath and controlling the temperature of the bath; and iv) applying an electric current to the electrically conductive substrate to provide a coating in the range of from 1 to 50 µm to further 0.005 to 2000 ppm of an additive compound containing zinc, cadmium, containing vanadium, sulfur, molybdenum, or a combination of two or more thereof, silver, mercury, thallium, lead, tin, arsenic, antimony, bismuth, or a combination of two or more thereof. Preferred are silver, cadmium, mercury, thallium, lead, arsenic, vanadium, sulfur or molybdenum.

For the preparation of cathodes having electrocatalytic coatings containing platinum group metals in a homogeneous phase,

i) degreasing the electrically conductive substrate, and ii) etching the electrically conductive substrate with an acid or electrolytically, iii) plating a plating bath containing metal ions suitable for forming a metal or metal alloy coating and a solution of soluble salts of platinum group metals, controlling the temperature of the bath; and iv) applying an electric current to the electrically conductive substrate to form a coating having a thickness of 1 to 50 µm, and adding to the electroplating bath an additional additive compound of zinc, cadmium, vanadium, sulfur, molybdenum or a combination of two or more thereof, silver, mercury, thallium, lead, tin, arsenic, antimony, bismuth or a combination of two or more thereof. Preferred are cadmium, thallium, lead, tin, arsenic, vanadium or molybdenum.

The aforementioned elements can be used in the form of their oxides, sulfides, sulfates, thiosulfates, halides preferably chlorides, oxyhalides preferably oxychlorides, metal salts of oxo acids, preferably alkali metal salts, nitrates, mixed salts thereof and complex salts thereof.

Also used are the following compounds: T1C1, Pb (NO _{3) 2,} SnCl _2, As ₂ O _3, Sb ₂ O _3, Bi ₂ O _3, PtCl _4, PdCl _2, CuCl _2, AgCl (NH _{3) 2,} AuCl ₃ , Fe (NO ₃ ) ₂ , (NH ₄ ) ₂ SO ₄ , Hg (NO ₃ ) ₂ , CdCl ₂ , VOCl ₂ , Na ₂ MoO ₄ , MoO ₃ , Na ₂ S ₂ O ₃ , Na ₂ S, Cd (NO ₃ ) ₂ , Bi (NO ₃ ) ₃ .

HU 215 459 Β

The electrocatalytic coating is applied to the support by methods known to those skilled in the art of electroplating. For example, the nickel electroplating bath may be a Watt bath (in the presence of boric acid or other buffering agent nickel chloride and sulfate), a stabilized or non-stabilized sulfamate bath, a Weisberg bath, a nickel chloride bath, a nickel chloride acetate bath and the like. Suitable amounts of soluble platinum group metal salts, as disclosed in the prior art patents, are dissolved in the solution, or alternatively, sufficient amounts of the aforementioned electrocatalytic particles are kept in suspension by mixing and, if necessary, adding a surfactant. Typically, when the metal support is a stretched nickel sheet or fabric, the soluble platinum group salt is ruthenium trichloride and the electrocatalytic material whose particles are kept in suspension is ruthenium dioxide.

Of course, when the coating is copper or silver based, or their alloys or other metals or their alloys, the galvanic or non-electrolytic baths used contain the base metal instead of nickel.

Although the thickness of the electrocatalytic coating, the percentage of platinum group metal present in the coating in the homogeneous phase or, alternatively, the amount and size of the electrocatalytic particles dispersed in the coating are not critical in themselves, they are essentially practical and economical. The coating generally has a thickness of 1-50 µιη, the amount of platinum group metal in the homogeneous phase is 0.1-50% by weight, and the dispersed particles are equally 0.01-150 µm in diameter and are 1-50% by weight.

The process of the present invention differs from the prior art described in the aforementioned Belgian Patent Nos. 848,548 and 4,465,580 in that the coating galvanic baths described above are suitable, in addition to the materials commonly used, for at least one of the additives mentioned above. is given. As a result of this addition, the coating contains different amounts of additives. In the following examples, the concentration of the additive elements in the coating can vary within wide limits depending on the coating conditions, in particular current density, temperature and bath pH, even if the compounds present in the coating bath are present in the same concentration. However, it has been found that the resistance of the electrode prepared in the above manner to poisoning during operation as a cathode is completely independent of the change in the amount of additives in the coating.

As regards the anti-toxicant action and chemical nature of the additives added to the coating, either as finely dispersed compounds in elementary state or in oxidized form, no full explanation can be given yet. To summarize, they are present in the form of hydrated oxides and iron microcrystals formed by low-noble additives such as Zn, Cd and V as their hydrated oxides or basic salts, and are characterized by the wetting of iron microcrystals formed by the coating surface, mercury droplets and electrodes. trigger a sharp change. In fact, due to the initial presence of platinum group metals or electrocatalytic particles in the formation of the coating, the deposition potential is not cathodic enough to allow the charge elements to become charged to the metal state.

As a result, the coatings of the present invention are fundamentally different from the prior art coatings, such as coatings in which a large amount of zinc is present in metal form and leached to increase porosity and active surface.

As for the more noble additives, especially platinum and palladium, these are sufficient to effectively suppress iron and mercury poisoning, even in small amounts, in the galvanic bath at 0.01 ppm or less in the coating.

The present invention relates to the controlled administration of the above additives.

Electrocatalytic coatings containing large amounts of platinum group metals, and in the extreme case coatings consisting solely of these elements, are readily deactivated when used as a cathode in contaminated alkaline solutions [see DE Grove, Platinun Metals Rev., 29 (3), 98-106 for ruthenium and platinum. (1985)].

The electrodes of the present invention are preferably used for electrolysis of alkali metal halides in electrolyte cells separated by gas and liquid permeable anodes and cathodes separated by a permeable diaphragm or ion exchange membrane; the membrane is substantially impermeable to the electrolyte flow and the cell contains a solution of an alkali metal hydroxide contaminated with iron and / or mercury as the catholyte.

In order to better illustrate the invention, the following are some of the most important examples. The examples are not limiting. In the following examples, for example, galvanic coating is used, but it will be apparent to those skilled in the art that non-electrolytic coating may be used.

Example 1

Different 0.71 mm samples of nickel wire of 0.1 mm diameter are degreased and etched with 15 wt% nitric acid for about 60 seconds. Using nickel samples as a carrier, they are electrolytically coated with the following composition:

nickel sulfate 210 g / l

nickel chloride 60 g / l

boric acid 30 g / l

- ruthenium oxide 4 g / l (calculated on the metal)

- additives (the type and concentration of additives are detailed in Table I)

HU 215 459 Β

The bath temperature is about 50 ° C and the current density is 100 A / m ² . The bath contains particles of ruthenium oxide with an average diameter of -2 μιη, the particles having a minimum diameter of 0.5 μιη and a maximum diameter of 5 μιη. The powder was kept in suspension by mechanical stirring and galvanizing was continued for 2 hours.

The resulting coating has a thickness of 25 µm and approximately 10% of the coating volume is comprised of ruthenium oxide particles uniformly dispersed in the nickel matrix. The surface of the coating contains oxide particles with a dendritic surface only partially covered with nickel.

The cathode potentials thus obtained were measured as a function of time at 90 ° C at a current density of 3 kA / m ^{2 in} 33% w / w sodium hydroxide solution contaminated with 50 ppm iron and 10 ppm mercury. The measured values were compared with those of a similar cathode in a bath without immunizing additives.

The results in Table I show a significant effect of catalytic aging, especially mercury-induced aging, on the cathode without additive. Catalytic aging has essentially been eliminated or significantly reduced in cathodes coated with nickel plating baths with the aforementioned additives.

The concentration of various additives in the electroplating bath and the concentrations of iron and mercury in the a

In the examples, 33% by weight of sodium hydroxide solution is given in ppm. The concentration of ppm is 1 parts per million parts, which corresponds to approximately 1 mg / l. The amount of the additives is given in the form of the corresponding element. For example, a concentration of 100 ppm thallium 15 µm (I) chloride means that the electroplating bath contains 117 ppm (-117 mg / l) of salt, which corresponds to a metal content of 100 ppm (-100 mg / l).

Table 1

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt or oxide ppm Initial One day 10 days Element pPM Ni + RuO ₂ - - - 1050 1050 1050 - - Ni + RuO ₂ - - - 1040 1060 1070 Fe 50 Ni + RuO ₂ - - - 1050 1150 1750 hg 10 Ni + RuO ₂ YOU T1C1 100 1050 1050 1050 Fe 50 Ni + RuO ₂ pb Pb (NO ₃ ) ₂ 100 1050 1050 1050 Fe 50 Ni + RuO ₂ sn SnCl ₂ 100 1050 1050 1050 Fe 50 Ni + RuO ₂ Dig As ₂ O ₃ 100 1050 1050 1050 Fe 50 Ni + RuO ₂ sb Sb ₂ O ₃ 100 1050 1050 1050 Fe 50 Ni + RuO ₂ bi Bi ₂ O ₃ 100 1050 1050 1050 Fe 50 Ni + RuO ₂ YOU T1C1 ₂ 100 1050 1050 1100 hg 10 Ni + RuO ₂ pb Pb (NO ₃ ) ₂ 100 1040 1040 1080 hg 10 Ni + RuO ₂ sn SnCl ₂ 100 1040 1040 1090 hg 10 Ni + RuO ₂ Dig As2O3 100 1040 1050 1090 hg 10 Ni + RuO ₂ sb Sb ₂ O ₃ 100 1040 1060 1120 hg 10 Ni + RuO ₂ bi Bi ₂ O ₃ 100 1040 1070 1130 hg 10

Some samples were tested for coating. A destructive assay, such as complete dissolution followed by a colorimetric or atomic absorption assay, and a non-destructive assay, such as an X-ray diffraction assay, were performed.

It has been found that in cases where the "additive effect" is due to the addition of lead, the lead is present in the coating in an amount of 100-1000 ppm. The amount of lead in the coating depends on the mixing intensity while maintaining other conditions unchanged.

Similarly, small amounts of additive in the range of 100-300 ppm have been found in tin coatings as additives. Higher concentrations occur at higher coating temperatures, such as 70 ° C instead of 50 ° C.

Example 2

After a suitable electrolytic purification, a nickel tissue sample of 0.1 mm diameter wire was suspended as described in Example 1, suspended in ruthenium oxide particles and in a solution as shown in Example II. soluble Pt, Pd,

Watt's Nickel electroplating bath containing Cu, Ag, or Au salts is activated to form an electrocatalytic coating.

The samples thus prepared are examined as a cathode at a temperature of 90 ° C and a current density of 3 kA / m ² ,

33 wt% NaOH, which may be poison5

EN 215 459 Β without substance or containing 10 ppm mercury. The result of the test is shown in Annex II. is shown in Table II.

Example 3

Some cathodes are prepared as described in Example 2, but mercury or iron salts are added to the nickel plating bath instead of platinum, palladium, copper, silver or gold salts.

The cathodes were permanently tested under the operating conditions described in Example 2 as a toxic substance in 33% w / w sodium hydroxide solution containing 50 ppm iron and 10 ppm mercury. Our results are shown in Annex III. See Table 1.

Example 4

A nickel tissue sample of 0.1 mm diameter wire was subjected, after suitable electrolytic purification, to suspension of ruthenium oxide particles as described in Example 1 and IV. Activated by forming a electrocatalytic coating using a Watt nickel electroplating bath containing the additives in Table II.

The samples were then examined as a cathode at 90 ° C in a 33 wt% sodium hydroxide solution, free of poison, or poisoned with 50 ppm iron or 10 ppm mercury at a current density of 3 kA / m ² . The cathode potentials as a function of electrolysis time are shown in Table IV. See Table 1.

II. spreadsheet

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt or oxide ppm Initial One day 10 days Element pPM Ni + RuO ₂ - - - 1050 1050 1050 - - Ni + RuO ₂ - - - 1050 1150 1750 hg 10 Ni + RuO ₂ Pt PtCl ₄ 0.01 1040 1040 1090 hg 10 Ni + RuO ₂ Pd PdCl ₂ 0.01 1050 1050 1100 hg 10 Ni + RuO ₂ Cu CuCl ₂ 0.01 1050 1050 1150 hg 10 Ni + RuO ₂ Branch AgCl (NH ₃ ) ₂ 0.01 1040 1040 1120 hg 10 Ni + RuO ₂ au AuC1 ₃ 0.01 1040 1040 1180 hg 10

III. spreadsheet

Cathode potential versus operating time

Coating Additive ad Cathode potential, mV (NHE) contamination 33% NaOH Element Salt pPM Initial One day 10 days Element ppm Ni + RuO ₂ - - - 1050 1050 1050 - - Ni + RuO ₂ - - - 1040 1060 1070 Fe 50 Ni + RuO ₂ - - - 1050 1150 1750 hg 10 Ni + RuO ₂ Fe The weight ratio of Fe (NO ₃ ) ₂ + (NH ₄ ) ₂ SO ₄ is 1:10 1 1040 1060 1070 Fe 50 Ni + RuO ₂ Fe The weight ratio of Fe (NO ₃ ) ₂ + (NH ₄ ) ₂ SO ₄ is 1:10 10 1040 1060 1060 Fe 50 Ni + RuO ₂ Fe The weight ratio of Fe (NO ₃ ) ₂ + (NH ₄ ) ₂ SO ₄ is 1:10 100 1040 1060 1070 Fe 50 Ni + RuO ₂ hg Hg (NO ₃ ) ₂ 1 1050 1150 1450 hg 10 Ni + RuO ₂ hg Hg (NO ₃ ) ₂ 10 1040 1070 1150 hg 10 Ni + RuO ₂ hg Hg (NO ₃ ) ₂ 100 1040 1080 1250 hg 10

HU 215 459 Β

ARC. spreadsheet

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt ppm Initial 30 minutes 60 minutes Element ppm Ni + RuO ₂ - - - 1000 1000 1000 - - Ni + RuO ₂ - - - 1000 1080 1116 Fe 50 Ni + RuO ₂ - - - 1000 1800 - hg 10 Ni + RuO ₂ CD CdCl ₂ 100 980 980 980 - - Ni + RuO ₂ V VOC1 ₂ 1 1010 1010 1010 - - Ni + RuO ₂ Mo Na ₂ MoO ₄ 10 1020 1020 1020 - - Ni + RuO ₂ CD CdCl ₂ 1 975 1320 - hg 10 Ni + RuO ₂ CD CdCl ₂ 10 950 1270 1310 hg 10 Ni + RuO ₂ CD CdCl ₂ 100 980 1080 1090 hg 10 Ni + RuO ₂ V VOC1 ₂ 1 1010 1080 1110 Fe 50 Ni + RuO ₂ V VOC1 ₂ 1 1000 1050 1105 hg 10 Ni + RuO ₂ V VOC1 ₂ 10 1010 1000 1200 hg 10 Ni + RuO ₂ Mo Na ₂ MoO ₄ 10 1020 1020 1060 Fe 50 Ni + RuO ₂ Mo Na ₂ MoO ₄ 1 1020 1100 1250 hg 10 Ni + RuO ₂ Mo Na ₂ Mo0 ₄ 5 1000 1080 1230 hg 10 Ni + RuO ₂ Mo Na ₂ Mo0 ₄ 10 1010 1020 1090 hg 10 Ni + RuO ₂ Mo MoOj 1 980 1160 1190 hg 10 Ni + RuO ₂ Mo MoOj 5 980 1130 1140 hg 10 Ni + RuO ₂ Mo MoOj 10 945 1120 1160 hg 10

Example 5 Quantity of materials used and appropriate

Nickel tissue samples are shown in Table V for the cathode potentials described in Example 1.

dosing, except that different amounts of sodium thiosulfate are used as an additive.

Table V.

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt ppm Initial 30 minutes 60 minutes Element pPM Ni + RuO ₂ - - - 940 980 980 - - Ni + RuO ₂ - - - 1000 1090 1150 Fe 50 Ni + RuO ₂ - - - 980 2000 - hg 10 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 10 990 1000 1040 Fe 50 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 100 990 1000 1020 Fe 50 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 500 960 960 960 Fe 50 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 10 970 1600 - hg 10 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 25 970 1550 - hg 10 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 50 970 1500 - hg 10 Ni + RuO ₂ s Na ₂ S ₂ O ₃ 100 950 1100 1580 hg 10

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Table V (continued)

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt ppm Initial 30 minutes 60 minutes Element ppm Ni + RuOj S 500 940 1050 1200 hg 10 Ni + RuOj S Na ₂ S ₂ O ₃ 1000 980 1030 1180 hg 10 Ni + RuO ₂ S Na ₂ S ₂ O ₃ 500 940 940 940 - -

Example 6

After a suitable electrolytic purification, a nickel tissue sample of 0.1 mm diameter wire was suspended as described in Example 1, suspended in ruthenium oxide particles and more than one, as in Example VI. is activated using a Watt nickel electroplating bath containing the dissolved compound of the exact additive in Table II. The samples were then tested as a cathode at 33 ° C in a 33% sodium hydroxide solution poisoned with 50 ppm iron and 10 ppm mercury at a current density of 3 kA / m ² . The results of the study are shown in Annex VI. See Table 1.

VI. spreadsheet

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) contamination 33% NaOH Element Salt pPM Initial One day 10 days Element pPM Ni + RuO ₂ - - - 1050 1050 1050 - - Ni + RuO ₂ - - - 1040 1060 1070 Fe 50 Ni + RuO ₂ - - - 1050 1150 1750 hg 10 Ni + RuO ₂ Sb + S Sb ₂ O ₃ 100 1040 1050 1040 Fe 50 Well ₂ S. 100 Ni + RuO ₂ Cd + Mo Cd (NO ₃ ) ₂ 100 1040 1040 1040 Fe 50 MoO ₃ 100 Ni + RuO ₂ Sb + S Sb ₂ O ₃ 100 1040 1050 1100 hg 10 Well ₂ S. 100 Ni + RuO ₂ Bi + Se Bi (NO ₃ ) ₃ 100 1040 1060 1100 hg 10 SeO ₂ 100

Example 7

A nickel tissue sample of 0.1 mm diameter wire is activated with a nickel-ruthenium electrocatalytic coating after appropriate electrolytic purification. The coating is made up of ruthenium trichloride corresponding to 1 g / l of ruthenium and in accordance with Annex VII. Table II is prepared in a Watt nickel electroplating bath containing additives. The coating conditions are the same

Example 1.

The resulting samples were tested as a cathode at 33 ° C in 50% ppm iron and 10 ppm mercury poisoned in 33% sodium hydroxide solution at a current density of 3 kA / m ² . The results are shown in Table VII.

See Table 1.

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VII. spreadsheet

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt ppm Initial One day 10 days Element pPM Ni-Ru - - - 1090 1090 1090 - - Ni-Ru - - - 1090 1180 1180 Fe 50 Ni-Ru - - - 1100 1650 2100 hg 10 Ni-Ru YOU T1C1 100 1090 1110 1150 Fe 50 Ni-Ru pb Pb (NO ₃ ) ₂ 100 1100 1100 1110 Fe 50 Ni-Ru sn SnCl ₂ 100 1100 1110 1130 Fe 50 Ni-Ru Dig As ₂ O ₃ 100 1100 1110 1120 Fe 50 Ni-Ru sb Sb ₂ O ₃ 100 1100 1110 1150 Fe 50 Ni-Ru bi Bi ₂ O ₃ 100 1090 1090 1120 Fe 50 Ni-Ru YOU T1C1 100 1090 1380 1750 hg 10 Ni-Ru pb Pb (NO ₃ ) ₂ 100 1090 1490 1750 hg 10 Ni-Ru sn SnCl ₂ 100 1100 1510 1780 hg 10 Ni-Ru Dig As ₂ O ₃ 100 1100 1420 1820 hg 10 Ni-Ru sb Sb ₂ O ₃ 100 1100 1600 1980 hg 10 Ni-Ru bi Bi ₂ O ₃ 100 1090 1590 1870 hg 10

Example 8

A nickel-ruthenium coating is prepared as described in Example 7 except that the additives used in Example 4 are used as additives.

The results obtained are the same as those obtained in Example 4.

Example 9

Following the procedure described in Example 7, a nickel tissue sample is activated, but unlike Example 8, the ruthenium trichloride galvanizing bath is activated with the VIII. The platinum, palladium, copper, silver gold salts described in Table II are added. VIII. Table 3 shows the cathode potentials measured at 90 ° C at a current density of 3 kA / m ² with 10 ppm mercury poisoned with sodium hydroxide.

VIII. spreadsheet

Cathode potential versus operating time

Coating Bath additive Cathode potential, mV (NHE) Impurity in 33% NaOH Element Salt pPM Initial One day 10 days Element pPM Ni-Ru - - - 1100 1090 1100 - - Ni-Ru - - - 1100 1650 2100 hg 10 Ni-Ru Pt PTCL, 0.01 1100 1150 1160 hg 10 Ni-Ru Pd PdCl ₂ 0.01 1100 1150 1170 hg 10 Ni-Ru Cu CuCl ₂ 0.01 1100 1140 1150 hg 10 Ni-Ru Branch AgCl (NH ₃ ) ₂ 0.01 1100 1060 1180 hg 10 Ni-Ru au AuCl ₃ 0.01 1100 1060 1060 hg 10

HU 215 459 Β

IX. spreadsheet

Cathode potential (mV, NHE) as a function of operating time for a catholyte containing 10 ppm mercury impurity ¹

Addition to the bath Cathode potential, mV (NHE) Initial 10 days 100 days 220 days after operating time No ² 1050 1750 2050 - TI ² 1050 1100 1200 1150 Pb ² 1040 1080 1130 1180 Sn ² 1040 1090 1200 1280 As ² 1040 1090 1070 1150 Sb ² 1040 1120 1200 1320 Bi ² 1040 1130 1190 1310 Pd ³ 1050 1100 1315 1810 Cd ⁴ 980 1200 1150 1190 Ref. A ⁵ 1140 - 1510 2030 Ref. B ⁶ 1150 - 1470 1910

¹ Operating conditions: 30% NaOH, 3KA / m ^2, 90 ° C Preparation ² Using the procedure of Example 1 using ³ Preparation procedure of Example 2 using ⁴ Preparation method as in Example 4. Preparation of ⁵ 3132 Using the procedure of Example 8 of German Patent No. 269 ⁶ Preparation using the procedure of Example 12 of German Patent 3132 269

Example 10

Use of the Cathode of the Invention for Electrolysis of Sodium Sulphate Three pieces of 0.71 mm nickel wire, 0.1 mm in diameter, were degreased and etched with 15% nitric acid for about 60 seconds. Two samples, 1 and 2, are then electrolytically coated in the galvanic bath as described in Example 1. The galvanic bath contains 100 ppm of lead dichloride for sample 1 and 100 ppm of arsenic trichloride for sample 2. Sample 3 is coated as described in Example 9, in which case the galvanic bath contains 1 ppm gold trichloride additive per metal.

The above three samples are used as membranes in a membrane cell for electrolysis of 20% w / w aqueous sodium sulfate solution. This solution is fed to an anode space containing a catalytic anode for oxygen depletion, which contains a titanium substrate and a suitable platinum group metal oxide coating known to those skilled in the art by heat decomposition of the precursor.

Into the cathode chamber containing the cathode described above is fed a 15 wt% sodium hydroxide solution containing 8 ppm of mercury. The anode space is separated from the cathode space by a Nafion ^R 324 cation exchange membrane (Du Pont de Nemours Co.). The cell

It is operated at 3000 amps / m ² at 80 ° C and the cathode potential is continuously monitored.

Below are the cathode potential values for the normal hydrogen electrode (NHE), expressed in mV for the time course of electrolysis.

ups: initial 2 days 10 days Sample 1 1030 1060 1060 Sample 2 1040 1030 1090 Sample 3 1030 1010 1040

The above data clearly demonstrate that the cathodes of the present invention are highly toxic to aging, even in the presence of high doses of mercury, even when operated in a cell used for electrolysis of a salt other than chloride.

Claims (12)

PATENT CLAIMS CLAIMS 1. A process for the galvanic production of catalytic electrodes from trace amounts of alkaline solutions containing toxic metals which can be used as a cathode, consisting of an electrically conductive support and a metal or metal alloy coating in which the electrocatalytic particles are dispersed; during the manufacturing process HU 215 459 Β i) degreasing the electrically conductive support, and ii) etching the electrically conductive support with acid or electrolytically, iii) electroconductive support comprising metal ions and suspended electrocatalytic particles having a mean diameter of 0.01 to 150 µm for forming a metal or metal alloy coating. immersing in a galvanizing coating bath and controlling the temperature of the bath; and iv) applying an electric current to the electrically conductive substrate to provide a coating having a thickness of 1 to 50 µm, further comprising adding to the galvanizing bath an additional additive compound containing zinc, containing cadmium, vanadium, sulfur, molybdenum or a combination of two or more of these. (Priority: December 14, 1984) A process for the electroplating of catalytic electrodes for the development of hydrogen from alkaline solutions containing trace amounts of toxic metals, which electrodes consist of an electrically conductive support and a metal or metal alloy coating in which the electrocatalytic particles are dispersed; during the manufacturing process i) degreasing the electrically conductive support, and ii) etching the electrically conductive support with acid or electrolytically, iii) electroconductive support comprising metal ions and suspended electrocatalytic particles having a mean diameter of 0.01 to 150 µm for forming a metal or metal alloy coating. immersing in a galvanizing coating bath and controlling the temperature of the bath; and iv) applying an electrical current to the electrically conductive substrate to a thickness of 1 to 50 µm, further comprising adding to the electroplating bath 0.0052000 ppm of an additional additive compound which The compound contains silver, mercury, thallium, lead, tin, arsenic, antimony, bismuth or a combination of two or more thereof. (Priority: October 17, 1985) The process according to claim 1, wherein the electrocatalytic material of the suspended particles is titanium, zirconium, niobium, hafnium, tantalum, metals of the platinum group, nickel, cobalt, tin and manganese metals, alone or in their alloys, oxides, mixed oxides, borides. in the form of their nitrides, carbides or sulphides. (Priority: December 14, 1984) The process according to claim 2, wherein the electrocatalytic material of the suspended particles is titanium, zirconium, niobium, hafnium, tantalum, metals of the platinum group, nickel, cobalt, tin and manganese metals, alone or in their alloys, their oxides, their mixed oxides, borides in the form of their nitrides, carbides or sulphides. (Priority: October 17, 1985) A process for the galvanic production of catalytic electrodes for the production of hydrogen from alkaline solutions containing trace amounts of toxic metal, which electrodes consist of an electrically conductive support and a metal or metal alloy coating which contains a homogeneous phase of the electrocatalytic metal of the platinum group; during the manufacturing process i) degreasing the electrically conductive substrate, and ii) etching the electrically conductive substrate with an acid or electrolyte, iii) plating a plating bath containing metal ions suitable for forming a metal or metal alloy coating and a solution of soluble salts of the platinum group metals, controlling the temperature of the bath; and iv) applying an electric current to the electrically conductive support to form a coating having a thickness of 1 to 50 µm, further comprising adding to the electroplating bath 0.0052000 ppm of an additional additive compound comprising zinc, cadmium, vanadium, sulfur, molybdenum, or a combination of two or more thereof. (Priority: December 14, 1984) A process for the galvanic production of catalytic electrodes for the production of hydrogen from alkaline solutions containing trace amounts of toxic metals, which electrodes consist of an electrically conductive support and a metal or metal alloy coating which contains a homogeneous phase of the platinum group electrocatalytic metal; during the manufacturing process i) degreasing the electrically conductive substrate, and ii) etching the electrically conductive substrate with an acid or electrolyte, iii) plating a plating bath containing metal ions suitable for forming a metal or metal alloy coating and a solution of soluble salts of the platinum group metals, controlling the temperature of the bath; and iv) applying an electric current to the electrically conductive substrate to provide a coating having a thickness of 1 to 50 µm, further comprising adding to the electroplating bath 0.0052000 ppm of an additional additive containing silver, mercury, thallium, containing lead, tin, arsenic, antimony, bismuth or a combination of two or more thereof. (Priority: October 17, 1985) 7. The process of claim 5 wherein the soluble salt of the metal of the platinum group is ruthenium trichloride. (Priority: December 14, 1984) HU 215 459 Β 8. The process according to claim 6, wherein the soluble salt of the metal of the platinum group is ruthenium trichloride. (Priority: October 17, 1985) Method according to any one of claims 1, 3, 5 or 7, characterized in that a galvanizing bath of nickel, copper or silver is used. (Priority: December 14, 1984) Method according to any one of claims 2, 4, 6 or 8, characterized in that a galvanizing bath of nickel, copper or silver is used. (Priority: October 17, 1985) A catalytic electrode for use as a cathode in the production of hydrogen from alkaline solutions containing trace amounts of toxic metals, characterized in that it is prepared according to any one of claims 1, 3, 5, 7 or 9. (Priority: December 14, 1984) A catalytic electrode for use as a cathode in the development of hydrogen from alkaline solutions containing trace amounts of toxic metals, characterized in that it is prepared according to any one of claims 2, 4, 6, 8 or 10. (Priority: October 17, 1985)